Every Island Fox Has a Story - Results from 2026 Island Fox Necropsy Workshop

 

At the Island Fox Necropsy Workshop in May, veterinary pathologist Leslie Woods, retired from UC Davis, led a group of island fox biologists, researchers, and others through the steps of an island fox necropsy (or autopsy) to understand the cause of the animals’ death. More about the Necropsy Workshop

Six island foxes from four islands were necropsied. Each tells a different and important story.

Parasitologist, Dr. Childress holds sample of parasites collected from island fox.

 

An island fox hit by a car is a snapshot of island fox health. For an island fox from San Nicolas Island, the immediate cause of death was car strike and a fractured skull. Further evaluation, however, revealed lungworm and that intestinal parasites (Spirocerca lupi) had traveled out of the fox’s intestines and through the blood vessels to other parts of his body. Even before its encounter with a vehicle, this island fox was critically ill. Previously, Spirocerca intestinal worms were considered a background health issue, incidental and typically not deadly. In 2026, however, nearly all island foxes on San Nicolas Island are infested with this worm and the average fox has a greater  amount of its intestine impacted. These worms can cause internal bleeding and infection. Across the islands, Spirocerca has become a more frequent cause of death for island foxes. The prevalence of this canine parasite is another reason people should not take pet dogs to the Channel Islands.

 

A San Clemente Island fox was discovered to have a swollen paw and inflammation around a rear leg bone. The necropsy revealed its forelegs were filled with cactus spines under the skin (see photo above). While this may have brought pain to the fox, the primary cause of death was kidney failure. Kidney or renal failure is a common cause of death for island foxes, yet the reason remains unknown. More research is needed to understand if there is a virus or bacterial connection or if something else makes island foxes vulnerable to kidney disease.

A Catalina Island fox was also found to have cactus spines in its tissues, but its cause of death was related to atrophy of its rear limb muscles which compromised its mobility and led to starvation. The cactus spines were not in the muscle. The cause of the muscle atrophy in this older fox remains unknown.

A second Catalina fox, a female in her prime, died of bacterial septicemia. Bacterial infection overwhelmed her heart and kidneys. Unfortunately, the initial source of the infection remains undetermined.

Despite concerted efforts to reduce island fox access to D3 rodenticide on San Clemente Island, another island fox accessed the material and was inadvertently poisoned. Knowing that rodenticide poisoning is still happening helps land managers make changes to protect other island foxes.

FIF President Mike Watling prepares protective gear

Friends of the Island Fox President Mike Watling and Treasurer Keri Dearborn helped necropsy a Santa Cruz Island fox. This 4-year-old male fox was the first fox mortality detected with the new digipeater collar system on Santa Cruz Island. Biologists were alerted through the automated system and the fox's body was found within 14 hours of his death.

Photos are taken throughout the necropsy to provide maximum information

His teeth showed hard wear for his 4 years. The good news was he appeared healthy, with no internal parasite problems or signs of disease, but this fox suffered an extreme abdominal trauma that caused internal organs to be pushed outside of his body. He was found up on a hillside a great distance from the road and there was no evidence to suggest car strike.

Did he fall from a cliffside or a tree? There were no other signs of physical trauma. Was he kicked or struck? He was in an area with few people. Was the weakness of his abdominal wall a genetic symptom that has yet to be identified? We don't know, but across the islands, everyone will be watching for similar unusual physical issues.

At the 2026 Necropsy Workshop, no new disease threats were identified. These necropsied island foxes provided important scientific information for the health of all island fox populations:

• Renal failure is a chronic island fox health problem; more research is needed to understand why. 
• Intestinal parasites and lungworm are growing concerns for all islands. 
• Prickly pear cactus spines may be more dangerous to island foxes than previously known. In the foxes examined, there was no walling off of the spines by the fox's immune system. Other island foxes have recently been found with plant matter that has migrated through their tissues into the lungs, causing death. Does greater investigation need to take place before prickly pear cactus is used in island restoration projects? 
• Investigation of viruses, fox immune systems, and thinking outside of the box on genetic vulnerabilities are needed going forward.  

Thank you to the Fresno Chaffee Zoo Wildlife Conservation Fund for a grant supporting island fox necropsies and pathology.

For more about the participating organizations in the 2026 Island Fox Necropsy Workshop 

Learning from an Island Fox's Death - Island Fox Necropsy Workshop 2026

Attendees viewing samples of parasites found in island foxes.

 

When an island fox dies, understanding the cause of death is important. Was the cause a disease that could threaten an entire island? Was the cause a human impact that could be avoided? Did a healthy appearing island fox meet with a sudden death that captured the actual state of its health like a photograph fixed in time? Was the cause of death unusual and greater understanding is needed?

In May, Friends of the Island Fox and the Santa Barbara Zoo hosted our second Island Fox Necropsy Workshop. Over the course of the day, six island foxes that died under different circumstances were examined. Physical specimens from various organs and parts of their bodies were collected and labeled for further evaluation at the California Animal Health and Food Safety Lab.

Veterinary pathologist Leslie Woods retired from UC Davis led the workshop with the assistance of parasitologist Dr. Jasmine Childress from the University of Wisconsin, and veterinary epidemiologist Dr. Jessica Sanchez from Utah State University and her graduate student veterinarian Kelsey Rayment.

The workshop goal was to teach field biologists how to identify probable causes of death and how to prepare specimens to be sent for further study. The workshop brought together representatives from the Channel Island land managers as well as veterinarians, technicians, and researchers from Cal State Long Beach, UC Riverside, USC, and the University of New Mexico.

The workshop helps researchers connect with how specimens are collected and builds holistic understanding of island fox physiology. Researcher Kimberly Schoenberger (USC) recently published on the brain size of island foxes working from skulls preserved at museums, but this was her first opportunity to directly encounter an island fox brain. Researcher, Eve Rowland (UNM), commented “I had a great experience. I have previous experience preparing specimens for museum collections, but it is pretty different from necropsy. … [I]t was helpful to understand how that process works.”

Dr. Childress shows collected intestinal parasites

 

Participants collected samples of various intestinal parasites and were able to examine and identify them under a microscope. It was a day of biological education, but also camaraderie and network building.

A huge thank you to FIF Board member Dr. Jessica Sanchez for spearheading the event, FIF Secretary Kris Chatari for organizing snacks and breaks, and to our co-hosts at the Santa Barbara Zoo, especially master organizer Nadya Seal and the veterinary team. Thank you also to the San Diego Zoo, UC Davis, and the CA Animal Health and Food Safety Lab for supplies and expertise.

Stay tuned for the findings from 6 island fox necropsies.

Hear directly from Dr. Woods about the importance of necropsy
See Dr. Sanchez give an island fox a health check
Researcher Eve Rowland will be presenting her work at the August 18, 2026 "Date with a Fox"

Training Biologists to Be Investigators When an Island Fox Dies

Dr. Jessica Sanchez overviews Necropsy Workshop

In November 2024, Friends of the Island Fox sponsored the 3rd "Island Fox Necropsy Workshop" in collaboration with the Santa Barbara and San Diego Zoos. This workshop was held to train island managers and field biologists to investigate island fox mortalities and determine cause of death. In this blog post, wildlife veterinarian and FIF board member, Dr. Jessica Sanchez, describes how necropsies are preformed and why they are such an important part of island fox conservation.

Necropsy tool kit

In the field of wildlife biology, understanding the reason animals die is an important first step to conserving populations. We must know what the problem is before we can start to address it. Tracking causes of death (AKA "mortality") also helps us learn more about the biology of a species–for example, the common diseases they get, their average life expectancy, the survival rate of their young, etc. By performing necropsies regularly on animals that die, we can: 1) learn what a normal, baseline mortality rate is and the common causes of death, and 2) more quickly detect if something abnormal is happening, such as the canine distemper outbreak on Santa Catalina Island.

The determination of cause of death is the expertise of pathologists, who dissect carcasses in what are called "necropsies" (the equivalent of a human autopsy). Epidemiologists study the patterns of disease in populations and help determine if a given mortality is expected for a population, or if something new/abnormal is happening, such as a newly introduced disease or an epidemic (higher than normal rates of disease).

 

Island fox with radio-tracking collar

On the Channel Islands, managers place radio-collars on a subset of the fox populations every year. These collars allow biologists to track animals and learn about their biology and behavior, but also to detect when they have died. The collars allow us to detect these deaths and retrieve the carcasses quickly, often from places where they would otherwise be hard to find (like deep in the woods, buried under vegetation, or even in a golden eagle nest!) Because we can retrieve these carcasses quickly, they are less likely to be degraded by the environment, giving pathologists the best chance to determine the cause of death.

Once in the pathology lab, scientists will look at the entire carcass for signs of the cause of death. They are true detectives, looking for signs of injury from being struck by a car, talon marks from a golden eagle, or pneumonia from infection. After examining the carcass visually (a "gross necropsy"), they collect tissues for microscopic examination. These tissues are stored in special chemicals that preserve the structure of the cells, so the pathologist can look at them under the microscope. This is how we identify bacterial or viral infections, abnormal protein buildup, cancers, and more. (Cancer in island foxes). They also collect swabs and blood samples to test for antibodies against disease ("serology"), use genetic material to identify pathogens like viruses and bacteria ("polymerase chain reaction" or PCR), or test for toxicants like rodenticides. For unusual or complicated cases, several experts may get involved, including virologists, immunologists, toxicologists, and epidemiologists.

Sometimes, sending a carcass off-island to a pathologist is not practical. In these cases, it is important that island biologists can perform "field necropsies" on the island. They can perform the gross necropsy and collect key samples to send off-island to the pathologist and laboratory for further investigation. These may not be as detailed as a necropsy from a pathologist, but they allow us to gather important information on cause of death and save tissues that could be important for future research.

Dr Leslie Woods leads the workshop

 

In November, twenty island biologists and researchers gathered at the Santa Barbara Zoo for training in performing necropsies. Drs. Leslie Woods (UC Davis) and Patty Gaffney (San Diego Zoo) are board certified veterinary pathologists who have worked with island foxes for decades. They led teams through performing full necropsies and collecting important tissues for further examination in the laboratory. We discussed common cause of death in island foxes and the signs to look for on gross necropsy. 

Accurately identifying sample slides

Participants also learned about sample storage and human safety when it comes to handling blood, tissues, and chemicals. FIF and the Island Fox Conservation Working Group plan to continue workshops like this periodically to train new staff and refresh the skills of field staff who are so important for the daily monitoring of these fox populations. They are our eyes and ears out on the island, looking for any new or emerging threats to the populations.

PPE is necessary to when working with animals that have died

Trainings like this highlight how important long-term monitoring and surveillance is for wildlife conservation, especially for a species such as the island fox which evolved isolated on an island and is under constant risk from introduced disease and invasive species. Radio-collaring foxes is critical for us to detect mortalities ASAP so we can retrieve the carcass as quickly as possible before signs of the cause of death start to degrade. It also helps us gather baseline information on survival rates of different age classes and sexes. Performing regular necropsies, even in the absence of an outbreak or other crisis, allows us to collect an invaluable archive of health and disease information about this species. Island fox researchers have built a database from hundreds of island fox necropsies going back 25+ years, which current and future researchers can use for studies on genetics, disease, reproduction, diet, and more. (Island Fox Research)

Thank you for supporting island fox research. Your support enables FIF to host workshops like this to train future generations of biologists to protect the island fox. - Dr. Jessica Sanchez

See Dr. Jessica Sanchez in action performing an island fox health check. 

A huge thank you to all those who helped facilitate this workshop:

Santa Barbara Zoo, San Diego Zoo, UC Davis and the CA Animal Health and Food Safety Lab